PureOS is a rolling release, based on Debian testing.
Purpose of Debian testing is as staging area for its long-term stable releases, and the repurposing as staging area for _rolling_ releases is problematic:
- Packages unsuitable for long-term stable releases (but fine for rolling releases) are kept out of Debian testing - by filing a so-called "RC bug" in the Debian bugtracker.
- During the finalizing of Debian stable releases - spanning maybe 4-6 months each 2-3 years - Debian testing is "frozen".
PureOS should have a well-defined way to include, and track continued relevancy of, specific packages from Debian unstable - when its (build-)dependencies are satisfied in Debian testing, and no _other_ RC bugs are filed against the package than those we specifically flag as rolling-release-acceptable.